The present invention relates generally to turbo compounds and, more specifically, to an electromagnetic, continuously variable transmission (CVT) power split turbo compound.
Mechanical turbo compound engines are well known, such as shown in U.S. Pat. No. 4,843,822, and generally include a power turbine placed in the exhaust gas stream, with a mechanical drive coupling through appropriate gear reduction and a fluid or spring coupling, driving the flywheel of the engine. In such turbo compound engines energy is recovered from the exhaust gas stream and re-applied to the engine output shaft reducing the brake specific fuel consumption, with the proviso that the rotational speed of the turbo compound is determined by the rotational speed of the engine (crankshaft). For a variety of reasons, it is desirable to be able to control the rotational speed of the power turbine independently of the engine's (crankshaft's) rotational speed.
Electric turbo compounds have been proposed as a solution to many of problems associated with mechanical turbo compounds. An electric turbo compound may include a high speed electrical generator connected directly to the power turbine, with associated power electronics either as a passive rectifier, or controlled inverter. Once the generated electrical power has been converted to DC (Direct Current) the electrical power may be stored or utilized immediately anywhere on the vehicle provided there is a suitable storage or electrical transmission. For the recuperated exhaust power to be utilized to drive the vehicle it must be reconverted to mechanical power.
While such a system may provide the advantages of variable turbo compound speed, it is at substantial cost in terms of system complexity and efficiency. As an example, a system dimensioned to allow the recuperation of 40 kW of exhaust energy and the application of the 100% of the recuperated energy to the crankshaft, would require a high-speed generator rated at 40 kW, power electronics associated with the conversion of the generated AC to DC rated at 40 kW, power electronics associated with the conversion of the intermediate DC to AC rated at 40 kW and an electric machine rated at 40 kW. The efficiency would also be reduced by each intermediate conversion.
By applying a power-split electric turbo compound, the majority of the power can be transmitted directly as in a mechanical turbo compound, with a minority portion of the recuperated energy being converted to electrical energy in such a manner that the turbo compound speed may be varied independently. In a power-split electric turbo compound, a Power Split Device (PSD) configuration is traditionally accomplished utilizing a mechanical epicyclic gear. Such systems tend to suffer from typical disadvantages of geared systems, such as the need for lubrication, gear wear, jamming, noise, vibration, etc. Moreover, gear ratios are constrained by the dimensions of the gears in the epicyclic gear. It is desirable to provide a system that can avoid some or all of these disadvantages.
In accordance with an aspect of the present invention, an electromagnetic, CVT power split turbo compound, comprises a turbo compound turbine driven by exhaust gases from an internal combustion engine, and a power split device comprising a magnetic gear arrangement. The magnetic gear arrangement comprises a high speed rotor comprising a first quantity of permanent magnets, a low speed rotor comprising a second quantity of permanent magnets, and a plural pole rotor between the high speed rotor and the low speed rotor. A first rotor of the high speed rotor, the low speed rotor, and the plural pole rotor comprises a mechanical input drive adapted to be driven by the turbine. A second rotor of the high speed rotor, the low speed rotor, and the plural pole rotor comprises a mechanical output drive. A third rotor of the high speed rotor, the low speed rotor, and the plural pole rotor is unconnected to a mechanical drive and comprises a controlling rotor for controlling a ratio of input drive angular velocity to output drive angular velocity.